Interesterification is one of effective means as a method for improving a fat. Conventionally, interesterification has been classified roughly into two methods, one is a chemical technique, that is,. a metal catalytic method, wherein random interesterification is performed by using a substance such as an alkali metal alcoholate, an alkali metal, an alkali metal hydroxide, etc. as a catalyst, and the other is an enzymatic interesterification method, wherein regiospecific or random interesterification is performed by using a lipase.
In the metal catalytic method and the enzymatic interesterification method, when the interesterification reaction is completed, an unreacted fatty acid ester remains, or diglycerides and monoglycerides or free fatty acids which are reaction by-products are produced. The presence of this fatty acid ester, diglycerides, monoglycerides and free fatty acids is known to have adverse effect on quality of an interesterified fat occasionally. For example, in a method for producing high value added symmetric triglycerides, a typical example thereof is cacao butter, obtained by enzymatic interesterification of triglycerides and a fatty acid ester using a lipase, and since the aforementioned unnecessary components significantly influence quality of high value added symmetric triglycerides, they should be removed as much as possible.
Usually, for producing 1,3-saturated-2-unsaturated triglycerides (hereinafter, sometimes, referred to as SUS), which are a major component of triglycerides, triglycerides (TG) and a fatty acid or its monohydric alcohol ester are subjected to an interesterification reaction with an enzyme. Since SUS triglycerides and fatty acids or their monohydric alcohol esters (FA) are produced, after the reaction, the fatty acids or their monohydric alcohol esters (FA) are distilled off by subjecting the reaction mixture to distillation-refining (purification). After distillation-refining, SUS triglycerides are concentrated by fractionation to increase a SUS component.